The present invention relates to an electronic still camera.
Electronic still cameras often employ contrast auto focus (AF) using an imaging device. While contrast AF does not require a special optical system or sensor, it suffers a slow operation because it seeks a focus point while driving the lens.
Jpn. Pat. Appln. KOKAI Publication No. 9-181954 and Jpn. Pat. Appln. KOKAI Publication No. 10-319310 disclose the technique that acquires image data by alternately moving apertures for splitting the pupil (a pair of pupil apertures) disposed in the optical path and computes the amount of defocus from image data obtained through the two actions in order to execute phase difference AF using the CCD of an imaging device. As this scheme can accomplish phase difference AF using an imaging device, the AF operation becomes faster.
Another type of electronic still camera that has a similar structure to that of a single-lens reflex camera which uses a silver film has also been put to a practical use.
General electronic still cameras have an LCD (Liquid Crystal Display) monitor and can display a picked-up image on this monitor in real time. A user may decide a composition using this monitor before taking a picture. When an AF operation is carried out using the scheme disclosed in the aforementioned prior arts, the presence of the apertures in the optical path prevent any display being made on the monitor during the AF operation.
A single-lens reflex type electronic still camera executes a focus detecting operation by guiding rays of light to a phase difference AF sensor via a quick return mirror, sub mirror and so forth placed on the optical axis of the imaging lens. Because the quick return mirror and sub mirror are located between the imaging device and the imaging lens, however, an image obtained by other operations than an imaging operation cannot be displayed on the LCD monitor.
Accordingly, it is an object of the present invention to provide an electronic still camera that has no image display break on the monitor screen while maintaining a fast AF operation which is ensured by the use of phase difference AF.